Heavily depends. If you want to use it as long-term cold storage you absolutely should not use SSDs, they’re losing data when left unpowered for too long. While HDDs are also not perfect in retaining data forever, they won’t fail as quickly when left on a shelf.
More reliable, less power draw than HDDs, faster and far more space efficient.
Unless you are data hoarding random torrents, 6 to 12 TB is plenty.
Heavily depends. If you want to use it as long-term cold storage you absolutely should not use SSDs, they’re losing data when left unpowered for too long. While HDDs are also not perfect in retaining data forever, they won’t fail as quickly when left on a shelf.